code: def get_expr_to_group_by(self) -> StructExpression:
      return self.facets
  
file_path: hail/hail/python/hail/ggplot/facets.py
imports: import abc
  import math
  from typing import Dict, Tuple
  from .geoms import FigureAttribute
  from .utils import n_partitions
  import hail
  from hail import Expression, StructExpression
label_desc: Use image node_id 2 for calling the FacetWrap obj's underlying member method code with example usage: obj.get_expr_to_group_by() and returns: self